


Switched places Sans

by prismatic_retro



Category: Undertale (Video Game)
Genre: Fluff and Smut, Kinky, Light Angst, Multi, Other, Polyamory, Romantic Fluff, Underfell Papyrus, Underfell Sans, Underswap Papyrus, Underswap Sans
Language: English
Status: In-Progress
Published: 2018-04-05
Updated: 2018-07-30
Packaged: 2019-04-18 16:56:14
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 2,979
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14217597
Author URL: https://archiveofourown.org/users/prismatic_retro/pseuds/prismatic_retro
Summary: Underswap Sans (Cobalt) and Underfell Sans (Rhubarb) switch universes as children. This story is based in the Underswap universe. It covers both sets of brother's relationships and how the Sans's switching places changed the brothers.





	1. Alternative Versions

**Author's Note:**

> This fic, has a lot of personal head cannons for both sets of brothers. Have fun, if there are any warnings I need to add let me know. Also I couldn't think of a title so yeah.

Sans took a deep breath and sighed. He was currently listening to an alternative version of himself, droning on about something. He was annoyed but he had no choice. Sans shifted slightly and he heard a pained whine come from his brother whose head was on his lap. Papyrus was hurt badly, so bad that he had blacked out from the pain.

Sans didn’t know what to do. Everything was happening so quickly. He was wary of this other Sans. He was unsure of his intentions and they were too vulnerable. Sans was tired from the constant use of magic. He was numbing Papyrus’s pain and using the rest to fuel a barrier to keep them safe. But on top of that he was also injured and hadn’t slept in two days.

He wouldn’t be able to fight, if the other decided to attack them. But then again there was no point. Sans had excepted that they were going to die. Either from their injuries or from the pack of dogs outside. All he had been doing was delaying it but now this other Sans was here. Making everything difficult.

“Hey other me, are you even listening?”

“Mweh, no.”

“Hmph, that is so rude.” He said glaring at Sans.

Sans sighed and said, “Look kid are you done talking? Cause we’re not going to be around much longer and I would like to enjoy it in peace.”

“Wait, w-what do you mean?” his happy demeaner faulting.

“If it’s not obvious were dying or going to once my magic runs out.”

“What!?! Oh, dear I-I didn’t even realize. I’m so sorry! What can I do to help?” He said rushing over to them.

Sans flinched and said “There isn’t anything you can do. If we don’t die from our wounds the dogs will kill us. I guess you haven’t noticed the fucking loud howls and bangs all around the house?”  
Just then a loud thud came from the area by the front door. The other Sans jumped and looked scared.

“We have to get out of here.”

Sans gave a pained sigh and said “There is nowhere to go, Asgore is dead and the underground is falling apart.”

“There is somewhere, my universe!”

Sans looked at him, he wasn’t sure about a different universe. But if there was a chance, he was going to take it.  
“Okay kid.” Sans said with a quick nod.

“Alright! I just need to set my machine and we’ll be good to go.”

Sans hadn’t noticed it before but around the other’s wrist was a bulky arm band thing. It had a large display screen and lots of nobs and buttons.  
“Okay, it’s all set, is there anything you want to take with you?”

Sans thought for a second and said “There’s a photo album on that shelf and our pet rock over on the table.”  
The other Sans quickly grabbed those items, walked over and sat down on the couch. Sans had pulled Papyrus up into his arms making room for his double.

“Okay, here we go!” The other him said hitting a button.

Sans took a deep breath and released the barrier. The dogs started breaking in through the door. The last thing he saw was them rushing in with bloodthirsty eyes. Then they were suddenly in a basement still sitting on the couch.

“Wow, that was close.” The other Sans said.

“Yeah, no shit, Sherlock.” Sans said refocusing his magic on Papyrus.

Sans gave a sigh of relief, no longer fueling the barrier made it easier to focus his magic. He watched as the pained look started to fade from his brother’s face. He gave a tired smile and turned to his counterpart.

“Is there any way we can get help? I’m not going to last forever and I need to know he is safe before I pass out.” Sans said.

“Oh, t-that’s right. Stay here I’ll go get some help!” The other Sans said running up the stairs.

“Like I could go anywhere.” Sans said with a snort.

It didn’t take long for the double to return with help. But at this point Sans was barely aware of it. Everything was blurry, their voices distant mumbles until everything went black.


	2. awake

**Summary for the Chapter:**

> Papyrus wakes up having no idea where he is or what has happened.

Papyrus had awoken to find himself in a hospital bed. He was confused and angry as he pushed himself up into a sitting position. Pain shot through his body as his head spun. A few minutes later the pain faded back to a dull throb. He then assessed the room, looking for any danger. He felt uneasy, everything seemed off. The room was a bright pale blue with a white trim, it even felt warm and inviting. Every medical room Papyrus had ever been in was cold, metallic, and smelled of blood and dust. This room smelled of flowers and clean sheets with a small hint of medical cleaner.

As he continued to look around he noticed the iv connected in between the bones of his left wrist where his magic flowed. He followed the cord up to see a bag that was labeled magic. Next to it was a machine that was monitoring something, it’s cord attached to his sternum. Other than this there were no other medical tools.

Papyrus was unsure what to do, he didn’t seem to be in danger. But he needed to get somewhere he knew was safe. That way he wouldn’t need to worry and could plan out his next move. As he contemplated this the door handle moved. Surprised he summoned a small sharpened bone which he concealed under the blanket.

‘I may be weak and in pain but I will still fight,’ he thought to himself.

He gripped the bone tightly as the door finally opened. A small form walked in to the room.

“Oh! You’re awake.”

Papyrus was shocked, the being talking to him looked like Sans. He had bright red eye lights which were currently sparkling. A large grin with sharp fangs and a pair of glasses over his eyes. This skeleton was shorter and thinner than Sans and his bones were unmarred. This only made Papyrus more concerned. This distorted copy of his brother was just standing there. Like he was waiting for something.

“Hey buddy, are you with me?”

Papyrus realized he was waiting for him to speak. He wasn’t sure what to say but answered with a simple yes.

“That’s good. Um, I’m going to go get Dr. Undyne so she can help you.”

And like that he was gone running out of the room leaving the door open. This was bad, Papyrus couldn’t fight Undyne. His only option was to run. He slowly swung his legs out of the bed. He was dizzy but he had to move, he grabbed hold of the Iv stand and pulled himself to his feet. Pain rushed through his body, knocking his non-existed breath out. He stood there for far too long trying to get use to the pain.

He didn’t have time for this, so slowly he pushed the Iv stand forward taking a few steps. He was shaking in agony but continued moving. The room felt huge to him as he pushed forward. He was halfway to the door when he heard his brother’s double. He wasn’t going to make it, he had to change his plan. He was fairly close to the wall, so he decided to use it as protection. This way Undyne couldn’t use all her attacks properly.

As he reached the wall he focused his energy, preparing to fight. He summoned a few bones as a weak attempt of a defense. His head spun from the movement but he did his best to balance. He heard their voices clearly now, they were just outside the door.

The odd Sans quickly stepped into the room and stopped. He was shocked to see Papyrus standing against the wall. Then Dr. Undyne stepped into the room. Papyrus was ready to fight her, but she was odd too. She was scared, even in his weak state he could sense it. She was wearing a lab coat, a pair of dorky glasses, and her hair was up in a bun.

“Hey, there bud.” The Sans said stepping forward.

Papyrus tensed, “Stay where you are, don’t come any closer.”

He stopped and said “We’re not going to hurt you. So please calm down.”

“Ha! As if. You brought her here to finish what she started.” He growled.

“What do you mean? She hasn’t done anything to you.”

“Liar, she tried to kill me! Like she killed Asgore!”

“Oh! This isn’t your Undyne.”

“What the fuck is that supposed to mean?”

“Okay, look. You’re not in your universe. The Undyne who attacked you isn’t here. This is my Undyne, she’s a scientist and doctor.” The Sans said calmly.

“Why should I believe you? This could just be some clever ploy to make me let my guard down.”

The pain began to surge through Papyrus’s body again. He had moved a bit further from the two.

“If we were going to hurt you, we would have done it by now. You have been passed out for a while. Plus Dr. Undyne was the one to patch you up.” The Sans said taking a step forward.

Papyrus wasn’t thinking to clearly because of the pain and maybe this odd Sans was correct. If there was another Sans then there could be another Undyne. But he needed to be sure.

“P-prove it to me.” Papyrus stuttered.

“Okay, what can we do that will prove it?”

“Summon an attack! Both of you.”

The two looked at him concerned but did as he asked. Papyrus knew if they summon an attack he could see their LV. Undyne couldn’t hide that from him. The other Sans quickly summon a small bone and held in his hand. The doctor took some time to summon a small ball of energy. He quickly looked at the LV, it wasn’t Undyne. They both quickly dismissed their attack.

“Okay, say I believe you, Undyne who might not be Undyne. What are you going to do?” Papyrus said a bit calmer.

“O-Oh, I-I am going to do a ch-checkup. Just to see h-how you’re doing and maybe get you some m-medicine for any pain.” She said timidly.

“See, she won’t hurt you. She just wants to help.”

Papyrus stared at them as he thought. The logic was sound, if there were two Sans then two Undyne would make sense. He had proof that this Undyne didn’t have the same LV, that his did. Also, she wasn’t loud and she was nervous. Which Undyne never was.

Papyrus took a deep breath and dismissed his attacks. He was still tense as the other Sans walk slowly toward him. His brother’s double gently grabbed his arm and helped him back to the bed. Once he was sitting comfortable, Dr. Undyne walked over and sat down on a stool next to him. She quickly checked to make sure his IV was still in his magic and reattached the cord to his sternum.

“Alright, h-how are you feeling?” Dr. Undyne said holding her clipboard closely.

“Like shit,” Papyrus said indigently.

“Oh! I-I’m sorry, that was a s-stupid question.”

“Yes, it was.”

“Hey be nice to Undyne. She’s just trying to help you.” The Sans interjected.

Papyrus gave this Sans a nasty look and said, “Fine, what’s your next question?”

“U-Um, on a scale of one t-to t-ten with ten being the highest. How much p-pain are you in?” she said looking up from her clipboard.

Papyrus thought for a moment and said “When I’m still it’s about a seven but when I move it’s a nine.”

“Okay, n-noted. Um, can you tell me w-what the last thing y-you remember before w-waking up here is?”

“Why?”

“I-It’s so we can figure out how l-long you’ve b-been hurt. This will h-help us to make your recovery f-faster.”

Papyrus sighed and looked away from them. “Fine, I remember my Undyne attacking me. Then she went after Sans…”

Papyrus paused, how could he have forgot Sans! His breathing picked up as he turned to them.

“Where’s Sans!?! Is he okay? I have to find him!” He said in full panic.

He began to push himself out of the bed. The other Sans pushed him back while telling him. “He’s in the room next you. He is currently asleep and he’s okay.”

“I-I need to see him!”

“You will when he wakes up later. We need you to stay calm.”

“You don’t understand! Please I need to see him.” Papyrus said as he burst into tears.

“O-Oh dear,” Undyne said covering her mouth with her hands.

“Okay! We’ll take you to see him. You just gotta calm down first!” His brother’s double yelled.

A wall of bones suddenly surrounded Papyrus, yet he was so upset he didn’t even notice. Both Undyne and the other Sans jumped in surprise.

“Who made Papyrus CRY!”

Papyrus looked over at the doorway through his tears. Sans was standing there with a look of pure anger. He quickly summoned several attacks which pointed at Undyne and his alternate self. He then lowered the wall surrounding his brother and slowly walked forward.

“Sans, you’re okay?” Papyrus sighed as tears continued to fall from his sockets.

“Yeah, I’m fine. Are you okay? I woke up to your panic and came over here as quickly as I could. Which if you couldn’t tell wasn’t very fast.” He said giving his best cheesy smile.

Before Papyrus could say anything, Sans had his arms around him.

“I’m okay, I was just worried.” He said burying his face into Sans chest.

“Well no need to worry now. I’m here.” He said giving Papyrus a kiss on the top of his skull.

Sans’s magic hummed gently helping Papyrus to calm down further.

“Alright now which one of these fuckers made you upset?” Sans said turning his face towards the two monsters. His attacks inches from their faces.

“It was the other you, though he didn’t mean too.”

The attacks disappeared and the two monsters relaxed a little. The room was quiet, Sans and Papyrus were staring at the others. Undyne was having trouble calming down.

“Mweh, sorry about that Dr. Undyne,” Sans said sympathetically “Didn’t mean to freak you out.”

“I-It’s okay. I just n-need to t-take a break.” She stammered standing up and walking out.

“As for you, other me. I told you the moment he woke up. No matter what time it was, to come get me first. So much of this could have been easily avoided!” Sans said aggressively.

“I did what I thought was best and that was to get Undyne. We needed to make sure his magic was stable.” The other Sans huffed.

“You’re an idiot. You saw how I reacted to seeing Dr. Undyne when I woke up. I nearly killed her! What did you expect Papyrus to do? Sit there and be happy to see someone who looks so much like the person that almost killed us. He could’ve hurt himself or worse!” Sans growled.

“Sans” Papyrus said pulling him closer, “It’s okay. Take deep breaths and let the anger pass.”

Sans looked at his brother and began to breath deeply. Allowing the anger to flow out of his mind and soul.

“Good job Sans. Now tell me what happened. I don’t remember anything after I saw Undyne start to attack you.” Papyrus said seriously.

Sans turned away from Papyrus and asked, “Do I have to talk about it now?”

“Yes, I need to know.”

“Fine” he sighed, “Undyne was going to kill you I stopped her but I lost control.”

“How many?”

“The majority of the crowd around us and a good portion of her rebellion.”

“What about her?”

“Mweh, her LV was too high for her too die. But she did lose her arm.” Sans chuckled darkly.

“How did she hurt you?” Papyrus said staring straight into Sans’s eye sockets.

“She hit me across the chest and my arms. Then she hit my legs. I fell to the ground next to you. In a panic I grabbed your arm and ported us back to the house.”

“Shit, how long was I out?” Papyrus asked.

“Two days, on the third he showed up.” Sans said gesturing to his alternative self.

“I-I’m so sorry Sans. I should have been able to protect you.” He said looking down at his hands.

“Russy,” Sans said gently moving Papyrus’s skull to face him. “Don’t worry, we’ll talk about it later. We’re safe now.”

Sans pulled him into a deep kiss helping wash away any self-hate that tried to cloud Papyrus’s mind. Papyrus sighed as he gently ran his fingers down Sans’s neck. Sans let out a soft moan pushing into his brother’s fingers. They were lost in each other’s embrace.

“Oh, my Toriel! STOP! This is inappropriate behavior. Not only are you in a public place but also in a place that has cameras!” The other Sans yelled covering his eyes.

“Mweh heh heh,” Sans laughed “Does this bother you?”

“Yes, and I would ask you to please cease this action.”

Sans stood up and got into his alternative self’s face. He gave a deep chuckle as he stared straight in his eyes.

“Or is it because it is making you feel so hot and bothered.”

Sans let out a breathy moan into the other’s face. Getting so close that their teeth were almost touching. His counterpart’s face became flushed red with embarrassment. He covered it with his hands and backed away from Sans.

“Sans,” Papyrus said giving a small laugh “Be nice.”

“Oh, Russy!” San whined “You know I was just playing.”

“Not everyone knows how to play that game.”

“Sigh!” Sans said as he posed as dramatically as he could.


End file.
